In a step of grinding and/or cutting a semiconductor wafer, a pressure sensitive adhesive sheet is used for the purpose of fixing the semiconductor wafer and protecting circuits and the like. As such a pressure sensitive adhesive sheet, there is a pressure sensitive adhesive sheet that comprises an energy ray curable pressure sensitive adhesive layer and has a strong adhesive strength during processing steps after attaching a semiconductor wafer thereto while the adhesive strength is reduced by irradiation of an energy ray when the pressure sensitive adhesive sheet is peeled off.
Such a pressure sensitive adhesive sheet is peeled off after predetermined processing steps are completed, but at the time of peeling, a static electrical charge called “peeling charge” may be generated between the pressure sensitive adhesive sheet and an adherend such as a semiconductor wafer and semiconductor chips (which may be simply referred to as a “chip” or “chips” hereinafter). Such a static electrical charge may cause breakage of semiconductor wafer/chips and circuits formed thereon. To prevent this, in a pressure sensitive adhesive sheet used when processing a semiconductor wafer, a quaternary ammonium salt compound having a low molecular weight is known to be added to a pressure sensitive adhesive thereby to allow the pressure sensitive adhesive sheet to have an antistatic property.
When a quaternary ammonium salt compound having a low molecular weight is used as an antistatic agent, however, problems may occur in that the compound bleeds out from the pressure sensitive adhesive sheet and the residual substances (particles) of the pressure sensitive adhesive contaminate the surface of an adherend such as a semiconductor wafer and chips.
In relation to the above, an antistatic pressure sensitive adhesive for an optical member is proposed as a pressure sensitive adhesive having an antistatic property, which uses as the pressure sensitive adhesive component a (meth)acrylic-based copolymer having a quaternary ammonium salt (see Patent Literature 1). In this pressure sensitive adhesive, the quaternary ammonium salt is introduced into the (meth)acrylic-based copolymer to allow a high molecular weight.